The fact that automotive-engineering components, such as gearbox systems, engine systems or brake systems, are controlled electronically to an increasing extent is generally known from the state of the art. To this end, there are integrated mechatronic controlling means (also referred to as on-site electronic systems) that can be created by the integration of the electronic control system and associated electronic components (e.g., sensors or valves) into the gearbox, the engine or the brake system, i.e., the electronic control system and the associated electronic components are not accommodated in a separate protected electronic-component space outside the gearbox, the engine or the brake system. In order to protect the electronic control system and the associated electronic components from environmental influences and mechanical, thermal and chemical stress, they are accommodated in special casings. In addition, said casings provide an important shielding function.
The usual structure for such integrated mechatronic controlling means consists of a ceramic substrate that includes the various electronic components of a central control unit. In order to enable peripheral components to be connected to the central control unit, the ceramic substrate is connected to rigid or flexible circuit boards or pressed screens by means of bond connections (e.g., aluminum thick-wire bond connections). Furthermore, the entire electronic-component space with the populated circuit carrier is coated with a silicone gel in order to protect the bond connections, the strip conductors and the components from moisture and other environmental influences.
When an integrated mechatronic controlling means is used as a gearbox control module, said module is accommodated in the gear oil pan so that it is completely surrounded by oil and electrically conductive contaminants contained in the oil. Said contaminants comprise contaminants that result from gear teeth abrasion, remnants of machining operations of manufacturing processes and/or from inadequate washing and cleaning processes of the gearbox casing and/or of the built-in components. In order to provide the necessary protection from such contamination, from damages and from strip-conductor or bond short circuits, a metallic, non-metallic or metallized casing cover is mounted onto a casing base plate of the gearbox control module and sealed hermetically.
In order to realize such units for gearbox control, casingless semiconductor components are mainly used. Said components are mounted on the ceramic substrate (circuit carrier) using conductive adhesives and are electrically contacted towards the circuit carrier by gold and aluminum wire bonding. The ceramic circuit carriers are realized in the form of thick-film circuits or as LTCC (Low Temperature Cofired Ceramics). With both ceramic circuit carrier technologies, strip conductors are produced by screen printing using highly argentiferous pastes. In addition, multifunctional end surfaces can be realized on the strip conductors of the circuit carrier in subsequent plating processes by means of a sequence of films (e.g., nickel, palladium and gold). At the same time, said end surfaces are suitable for connecting techniques, such as soldering, gold or aluminum wire bonding, and using conductive silver adhesives. These two ceramic circuit carrier technologies are suitable for high operating temperatures in or on the gearbox.
For heat dissipation (heat removal) of the circuit, the ceramic circuit carriers are adhesively bonded on metallic base plates or casing parts by means of a thermally conductive adhesive.
Furthermore, there are technical solutions that comprise a circuit board instead of the ceramic substrate.
Mounting the casingless semiconductor components on the circuit board by means of conductive silver adhesives and wire bonding is also referred to as chip-on-board (COB). According to this method, the semiconductor components are protected from environmental influences, such as moisture, by means of a singular glob top that is individually applied to the components. The glob top material is a polymeric resin, typically an epoxy resin with fillers such as silicon oxide. The thermal expansion of the glob top material is adapted to the thermal expansion of the circuit board, wherein the glob top material has a high modulus of elasticity. Chip-on-board applications are designed for moderate reliability requirements and temperature requirements (e.g., between −40° C. and 85° C.), whereas the typical operating-temperature range of gearbox controllers extends from −40° C. to +160° C. and higher temperatures. No applications are known for such operating-temperature ranges.
The fact that heat is removed from the components by means of thermal vias is also known from the state of the art. When mounting casingless semiconductor components (also referred to as bare dice) onto a circuit carrier (circuit board), the components (casingless semiconductor components) are conductively mounted, together with passive components, onto the surface of the circuit board by means of adhesive bonding or soldering. The component is electrically contacted to the circuit carrier by means of wire bonding. A standard circuit board technique (multilayer technique) uses thermal vias for facilitating the heat dissipation of the components, in particular of active components, said thermal vias being drilled mechanically. Thermal vias are used both for components that are accommodated in casings and for casingless components, wherein heat flows to the bottom of the circuit board via the thermal vias. A copper pad arranged on the bottom of the circuit board transfers the heat to a heat sink via the thermally conductive adhesive.
DE 10 2007 032 535 A1 describes an electronic module having a casing cover and at least one multilayer circuit board as an electrical connection between the interior of the casing and components that are arranged outside the casing. The multilayer circuit board is a circuit carrier for electronic components of a central electronic control system. At the same time, it is a thermal connection to a base plate for an integrated mechatronic gearbox controller. The circuit board has vias for providing a thermal connection to the base plate and for providing an electronic connection to the components that are arranged outside the casing.
In the integrated gearbox controllers, but also in an externally mounted control unit, the electronic components on the circuit carriers and the junctions between the electronic components and the strip conductors on the circuit carrier or between the electronic components themselves are exposed to very high levels of stress caused by temperature and vibrations. It is therefore necessary to adapt the circuit board to the requirements of the control units for gearbox control.